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David Leadley

University of Warwick, Physics, Faculty Member

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Head of Department of Physics
Physics, technology and materials science related to thin layered structures grown from silicon, germanium and their alloys.

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Mogadalai Gururajan

IIT Bombay

Arizona State University

Suseendran Jayachandran

IMEC

University of Virginia

Moscow State University

Elvira Fortunato

Universidade Nova de Lisboa

University of Illinois at Urbana-Champaign

Massachusetts Institute of Technology (MIT)

University of Dr moulay taher

Nanyang Technological University

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Papers by David Leadley

Fractional Quantum Hall Effect Measured in a Spin Degenerate Electron Gas

The influence of spin on the Fractional Quantum Hall Effect is investigated in GaAs-GaAlAs hetero... more The influence of spin on the Fractional Quantum Hall Effect is investigated in GaAs-GaAlAs heterojunctions in a filling factor region where both spin states of the lowest Landau level are occupied. When the single particle spin splitting is reduced by hydrostatic pressure features at even numerator fractions are enhanced while those with odd numerators are diminished. This is due to the existence of spin- and Landau gaps in the composite Fermion energy spectrum. In this paper the influence of spin splitting on the Fractional Quantum Hall Effect (FQHE) is studied experimentally by reducing the energy difference between electron states of spin up and spin down with hydrostatic pressure. 1 The results are interpreted in the composite Fermion (CF) framework. Usually only one spin state is considered, i.e. the electrons are treated as spinless particles or in the limit of infinite spin splitting. Then the FQHE can be interpreted as an integer QHE of spinless CFs and all the features seen...

Long Wavelength {greater than or equal to} 1.9 μm Germanium for Optoelectronics Using Process Induced Strain

by Philippe Velha and David Leadley

Tuning the electroluminescence of n-Ge LEDs using process induced strain

by Philippe Velha and David Leadley

IEEE International Conference on Group IV Photonics GFP, 2012

ABSTRACT LEDs are reported from Ge-on-Si in which process induced strain has increased the emissi... more

Long wavelength> 1.9 um germanium for optoelectronics using process induced strain

by Philippe Velha and David Leadley

Direct band-gap electroluminescence from strained n-doped germanium diode

by Philippe Velha and David Leadley

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT The fabrication and characterisation of LED structures made of Ge grown on Si substrates... more ABSTRACT The fabrication and characterisation of LED structures made of Ge grown on Si substrates is reported. The structures are circular mesa of strained n-Ge etched down to an undoped buffer of Ge. The electroluminescence exhibit average power levels at 1.7 mu m of 10 mu W, many orders of magnitude larger than the nW previously reported. 3 individual mechanisms of emission are identified which can be used to interpret the results encountered in other publications. This work potentially opens the route for integrated source of light and photodetector sabove 1.6 mu m on Si with applications for lab-on-a-chip and healthcare. (C) 2011 Optical Society of America

Ohmic contacts to n-type germanium with low specific contact resistivity

by Philippe Velha and David Leadley

Applied Physics Letters, 2012

Process induced strain bangap reduction in Germanium nanostructures

by Philippe Velha and David Leadley

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT We studied the photoluminescence of tensile strained germanium nanostructures. Sub-micro... more ABSTRACT We studied the photoluminescence of tensile strained germanium nanostructures. Sub-micron gratings and pillars were fabricated before being coated with strained silicon nitride films. Using different deposition conditions and different sizes of structures the stress in the nanostructures can be controlled. The measured optical properties of the samples show that the direct band-gap is shifted drastically towards higher wavelengths over 1.9 μm. This local control of the stress in germanium nanostructures opens the route for both emitters and photodetectors above 1.6 μm wavelength which are not easily available and also potentially towards a germanium laser.

Long Wavelength≥ 1.9 μm Germanium for Optoelectronics Using Process Induced Strain

by Philippe Velha and David Leadley

Strained germanium nanostructures on silicon emitting at >2.2 µm wavelength

by Philippe Velha and David Leadley

10th International Conference on Group IV Photonics, 2013

ABSTRACT The photoluminescence of process-induced tensile strained nanostructures fabricated usin... more

Physics World, 1996

Analysis of surface defects in Si 1− y C y epilayers formed by the oversaturation of carbon

Semiconductor Science and Technology, 2015

Disilane and trimethylsilane as precursors for RP-CVD growth of Si<inf>1−y</inf>C<inf>y</inf> epilayers on Si(001)

EUROSOI-ULIS 2015: 2015 Joint International EUROSOI Workshop and International Conference on Ultimate Integration on Silicon, 2015

Flat single crystal Ge membranes for sensors and opto-electronic integrated circuitry

Solid-State Electronics, 2014

ABSTRACT A thin, flat and single crystal membrane on which to mount sensors is generally required... more ABSTRACT A thin, flat and single crystal membrane on which to mount sensors is generally required for integration with electronics through standard silicon processing technology. We present an approach to producing single crystal membranes of germanium with in-built tensile strain, which serves to keep the membrane flat and ripple free, and demonstrate a 600 nm thick, free-standing 1 mm2 Ge membrane. We convert the fabrication technique into an integrated-circuit compatible wafer scale process to produce 60 nm thin membranes with large areas of 3.5 mm2. The single crystal Ge membrane provides an excellent platform for further epitaxial growth or deposition of materials.

Electrical activation of nitrogen heavily implanted 3C-SiC(100)

Applied Surface Science, 2015

A degenerated wide bandgap semiconductor is a rare system. In general, implant levels lie deeper ... more A degenerated wide bandgap semiconductor is a rare system. In general, implant levels lie deeper in the bandgap and carrier freeze-out usually takes place at room temperature. Nevertheless, we have observed that heavily doped n-type degenerated 3C-SiC films are achieved by nitrogen implantation level of ~6x10 20 cm -3 at 20K. According to temperature dependent Hall measurements, nitrogen activation rates decrease with the doping level from almost 100% (1.5x10 19 cm -3 , donor level 15meV) to ~12% for 6x10 20 cm -3 . Free donors are found to saturate in 3C-SiC at ~7x10 19 cm -3 . The implanted film electrical performances are characterized as a function of the dopant doses and post implantation annealing (PIA) conditions by fabricating Van der Pauw structures. A deposited SiO 2 layer was used as the surface capping layer during the PIA process to study its effect on the resultant film properties. From the device design point of view, the lowest sheet resistivity (~1.4mΩ.cm) has been observed for medium doped (4x10 19 cm -3 ) sample with PIA 1375°C 2h without a SiO 2 cap.

Si<sub>1-x</sub>C<sub>x</sub>/Si(001) Heterostructures for Use in Schottky Diode Rectifiers Demonstrating High Breakdown Voltage and Negligible Leakage Current

Materials Science Forum, 2015

Optical modulation using the silicon platform

Silicon Photonics VIII, 2013

ABSTRACT Optical modulator devices in silicon have experienced dramatic improvements over the las... more ABSTRACT Optical modulator devices in silicon have experienced dramatic improvements over the last decade, with data rates demonstrated up to 50Gb/s and ultra-lower power consumption with a few fJ/bit[1]. However a significant need exist for high speed low power devices with a small footprint and broadband characteristics with extinction ratio above 5dB. Here we describe the work within the UK silicon photonics program, which has led to the fabrication and preliminary results of novel nano cavity optical architecture as well as self-aligned pn junction structures embedded in a silicon rib waveguide with an active length in the millimetre range producing high-speed optical phase modulation whilst retaining a high extinction ratio.

P-Si/sub 0.3/Ge/sub 0.7/and p-Si/sub 0.2/Ge/sub 0.8/ MOSFETs of enhanced performance

Electrical Performance of Electrical Packaging (IEEE Cat. No. 03TH8710), 2003

Measurements of current drive in p-Si1-xGex MOSFETs, with x=0.7 and 0.8, reveal an enhancement ra... more Measurements of current drive in p-Si1-xGex MOSFETs, with x=0.7 and 0.8, reveal an enhancement ratio of over 2 times as compared to a Si device at an effective channel length of 0.55 μm. They also show a lower knee voltage in output I-V characteristics while retaining similar values of drain induced barrier lowering, subthreshold swing, and off current for devices with an Sb-doped punch-through stopper.

Thermally grown GeO<inf>2</inf> on epitaxial Ge on Si(001) substrate

2013 14th International Conference on Ultimate Integration on Silicon (ULIS), 2013

ABSTRACT We show good quality (GeO2) layer grown on epitaxial germanium on a Si substrate. The ox... more

Reverse terrace graded Si<inf>1−x</inf>Ge<inf>x</inf>/Ge/Si(001) virtual substrates grown using RP-CVD on on-axis and 6° off-axis substrates for future developments in III-V materials integration

EUROSOI-ULIS 2015: 2015 Joint International EUROSOI Workshop and International Conference on Ultimate Integration on Silicon, 2015

Using platinum silicide as a superconductor for silicon electron coolers

2013 14th International Conference on Ultimate Integration on Silicon (ULIS), 2013

An electron cooling junction using platinum silicide as a superconductor contact is demonstrated ... more An electron cooling junction using platinum silicide as a superconductor contact is demonstrated for the first time. The junction shows encouraging electrical characteristics and a fit to a standard cooling model predicts cooling from 100 mK to 50 mK for a test device. Silicides have been widely used in the semiconductor industry because of their reliability and reduced contact resistance; hence this technology could find wider application in a silicon-based electron refrigerator.

Fractional Quantum Hall Effect Measured in a Spin Degenerate Electron Gas

The influence of spin on the Fractional Quantum Hall Effect is investigated in GaAs-GaAlAs hetero... more The influence of spin on the Fractional Quantum Hall Effect is investigated in GaAs-GaAlAs heterojunctions in a filling factor region where both spin states of the lowest Landau level are occupied. When the single particle spin splitting is reduced by hydrostatic pressure features at even numerator fractions are enhanced while those with odd numerators are diminished. This is due to the existence of spin- and Landau gaps in the composite Fermion energy spectrum. In this paper the influence of spin splitting on the Fractional Quantum Hall Effect (FQHE) is studied experimentally by reducing the energy difference between electron states of spin up and spin down with hydrostatic pressure. 1 The results are interpreted in the composite Fermion (CF) framework. Usually only one spin state is considered, i.e. the electrons are treated as spinless particles or in the limit of infinite spin splitting. Then the FQHE can be interpreted as an integer QHE of spinless CFs and all the features seen...

Long Wavelength {greater than or equal to} 1.9 μm Germanium for Optoelectronics Using Process Induced Strain

by Philippe Velha and David Leadley

Tuning the electroluminescence of n-Ge LEDs using process induced strain

by Philippe Velha and David Leadley

IEEE International Conference on Group IV Photonics GFP, 2012

ABSTRACT LEDs are reported from Ge-on-Si in which process induced strain has increased the emissi... more

Long wavelength> 1.9 um germanium for optoelectronics using process induced strain

by Philippe Velha and David Leadley

Direct band-gap electroluminescence from strained n-doped germanium diode

by Philippe Velha and David Leadley

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT The fabrication and characterisation of LED structures made of Ge grown on Si substrates... more ABSTRACT The fabrication and characterisation of LED structures made of Ge grown on Si substrates is reported. The structures are circular mesa of strained n-Ge etched down to an undoped buffer of Ge. The electroluminescence exhibit average power levels at 1.7 mu m of 10 mu W, many orders of magnitude larger than the nW previously reported. 3 individual mechanisms of emission are identified which can be used to interpret the results encountered in other publications. This work potentially opens the route for integrated source of light and photodetector sabove 1.6 mu m on Si with applications for lab-on-a-chip and healthcare. (C) 2011 Optical Society of America

Ohmic contacts to n-type germanium with low specific contact resistivity

by Philippe Velha and David Leadley

Applied Physics Letters, 2012

Process induced strain bangap reduction in Germanium nanostructures

by Philippe Velha and David Leadley

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT We studied the photoluminescence of tensile strained germanium nanostructures. Sub-micro... more ABSTRACT We studied the photoluminescence of tensile strained germanium nanostructures. Sub-micron gratings and pillars were fabricated before being coated with strained silicon nitride films. Using different deposition conditions and different sizes of structures the stress in the nanostructures can be controlled. The measured optical properties of the samples show that the direct band-gap is shifted drastically towards higher wavelengths over 1.9 μm. This local control of the stress in germanium nanostructures opens the route for both emitters and photodetectors above 1.6 μm wavelength which are not easily available and also potentially towards a germanium laser.

Long Wavelength≥ 1.9 μm Germanium for Optoelectronics Using Process Induced Strain

by Philippe Velha and David Leadley

Strained germanium nanostructures on silicon emitting at >2.2 µm wavelength

by Philippe Velha and David Leadley

10th International Conference on Group IV Photonics, 2013

ABSTRACT The photoluminescence of process-induced tensile strained nanostructures fabricated usin... more

Physics World, 1996

Analysis of surface defects in Si 1− y C y epilayers formed by the oversaturation of carbon

Semiconductor Science and Technology, 2015

Disilane and trimethylsilane as precursors for RP-CVD growth of Si<inf>1−y</inf>C<inf>y</inf> epilayers on Si(001)

EUROSOI-ULIS 2015: 2015 Joint International EUROSOI Workshop and International Conference on Ultimate Integration on Silicon, 2015

Flat single crystal Ge membranes for sensors and opto-electronic integrated circuitry

Solid-State Electronics, 2014

ABSTRACT A thin, flat and single crystal membrane on which to mount sensors is generally required... more ABSTRACT A thin, flat and single crystal membrane on which to mount sensors is generally required for integration with electronics through standard silicon processing technology. We present an approach to producing single crystal membranes of germanium with in-built tensile strain, which serves to keep the membrane flat and ripple free, and demonstrate a 600 nm thick, free-standing 1 mm2 Ge membrane. We convert the fabrication technique into an integrated-circuit compatible wafer scale process to produce 60 nm thin membranes with large areas of 3.5 mm2. The single crystal Ge membrane provides an excellent platform for further epitaxial growth or deposition of materials.

Electrical activation of nitrogen heavily implanted 3C-SiC(100)

Applied Surface Science, 2015

A degenerated wide bandgap semiconductor is a rare system. In general, implant levels lie deeper ... more A degenerated wide bandgap semiconductor is a rare system. In general, implant levels lie deeper in the bandgap and carrier freeze-out usually takes place at room temperature. Nevertheless, we have observed that heavily doped n-type degenerated 3C-SiC films are achieved by nitrogen implantation level of ~6x10 20 cm -3 at 20K. According to temperature dependent Hall measurements, nitrogen activation rates decrease with the doping level from almost 100% (1.5x10 19 cm -3 , donor level 15meV) to ~12% for 6x10 20 cm -3 . Free donors are found to saturate in 3C-SiC at ~7x10 19 cm -3 . The implanted film electrical performances are characterized as a function of the dopant doses and post implantation annealing (PIA) conditions by fabricating Van der Pauw structures. A deposited SiO 2 layer was used as the surface capping layer during the PIA process to study its effect on the resultant film properties. From the device design point of view, the lowest sheet resistivity (~1.4mΩ.cm) has been observed for medium doped (4x10 19 cm -3 ) sample with PIA 1375°C 2h without a SiO 2 cap.

Si<sub>1-x</sub>C<sub>x</sub>/Si(001) Heterostructures for Use in Schottky Diode Rectifiers Demonstrating High Breakdown Voltage and Negligible Leakage Current

Materials Science Forum, 2015

Optical modulation using the silicon platform

Silicon Photonics VIII, 2013

ABSTRACT Optical modulator devices in silicon have experienced dramatic improvements over the las... more ABSTRACT Optical modulator devices in silicon have experienced dramatic improvements over the last decade, with data rates demonstrated up to 50Gb/s and ultra-lower power consumption with a few fJ/bit[1]. However a significant need exist for high speed low power devices with a small footprint and broadband characteristics with extinction ratio above 5dB. Here we describe the work within the UK silicon photonics program, which has led to the fabrication and preliminary results of novel nano cavity optical architecture as well as self-aligned pn junction structures embedded in a silicon rib waveguide with an active length in the millimetre range producing high-speed optical phase modulation whilst retaining a high extinction ratio.

P-Si/sub 0.3/Ge/sub 0.7/and p-Si/sub 0.2/Ge/sub 0.8/ MOSFETs of enhanced performance

Electrical Performance of Electrical Packaging (IEEE Cat. No. 03TH8710), 2003

Measurements of current drive in p-Si1-xGex MOSFETs, with x=0.7 and 0.8, reveal an enhancement ra... more Measurements of current drive in p-Si1-xGex MOSFETs, with x=0.7 and 0.8, reveal an enhancement ratio of over 2 times as compared to a Si device at an effective channel length of 0.55 μm. They also show a lower knee voltage in output I-V characteristics while retaining similar values of drain induced barrier lowering, subthreshold swing, and off current for devices with an Sb-doped punch-through stopper.

Thermally grown GeO<inf>2</inf> on epitaxial Ge on Si(001) substrate

2013 14th International Conference on Ultimate Integration on Silicon (ULIS), 2013

ABSTRACT We show good quality (GeO2) layer grown on epitaxial germanium on a Si substrate. The ox... more

Reverse terrace graded Si<inf>1−x</inf>Ge<inf>x</inf>/Ge/Si(001) virtual substrates grown using RP-CVD on on-axis and 6° off-axis substrates for future developments in III-V materials integration

EUROSOI-ULIS 2015: 2015 Joint International EUROSOI Workshop and International Conference on Ultimate Integration on Silicon, 2015

Using platinum silicide as a superconductor for silicon electron coolers

2013 14th International Conference on Ultimate Integration on Silicon (ULIS), 2013

An electron cooling junction using platinum silicide as a superconductor contact is demonstrated ... more An electron cooling junction using platinum silicide as a superconductor contact is demonstrated for the first time. The junction shows encouraging electrical characteristics and a fit to a standard cooling model predicts cooling from 100 mK to 50 mK for a test device. Silicides have been widely used in the semiconductor industry because of their reliability and reduced contact resistance; hence this technology could find wider application in a silicon-based electron refrigerator.